ec429 comments on What is Evidence? - Less Wrong

60 Post author: Eliezer_Yudkowsky 22 September 2007 06:43AM

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Comment author: Will_Sawin 16 September 2011 03:49:48AM 2 points [-]

Classical probability preserves amplitude, quantum preserves |amplitude|^2.

They're different things, and they could, potentially, be even more different.

Comment author: ec429 16 September 2011 03:58:19AM 1 point [-]

Um, but isn't that just a convention? Why should we treat the "amplitude" of a classical probability as being the probability?

Does the problem have something to do with the extra directionality quantum probabilities have by virtue of the amplitude being in C? (so that |0> and (-1*|0>) can cancel each other out)

Comment author: Will_Sawin 21 September 2011 04:46:46AM 1 point [-]

Classical probability transformations preserve amplitude and quantum ones preserve |amplitude|^2. That's not a whole reason, but it's part of one.

Yes, that's part of the difference. Quantum transformations are linear in a two-dimensional wave amplitude but preserve a 1-dimensional |amplitude|^2. Classical transformations are linear in one-dimensional probability and preserve 1-dimensional probability.

Comment author: ec429 21 September 2011 12:46:19PM 0 points [-]

Ah, I get it now, thanks!

(Copenhagen is still wrong though ;)